Heat exchange apparatus for exhaust gas

ABSTRACT

In an EGR module including a tank, an EGR gas cooler arranged on the downstream side of the flow of the exhaust gas inside the tank, a bypass arranged in parallel with the EGR gas cooler and an exhaust gas flow rate ratio regulating valve arranged on the downstream side of the flow of the exhaust gas of the EGR gas cooler and the bypass, wherein the inlet port is arranged at a position of the tank at which at least an area of a portion of the inlet port opposing the bypass is greater than an area of a portion of the inlet port opposing the EGR gas cooler.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a heat exchange apparatus, for an exhaust gas, that performs heat exchange between an exhaust gas, resulting from the combustion in an internal combustion engine, and a cooling fluid and is applied to an exhaust gas recirculation apparatus generally called an EGR apparatus.

2. Description of the Related Art

An apparatus having an EGR gas cooler and bypass is known as a heat exchange apparatus for an exhaust gas, as will be later described (refer to the pamphlet of International Publication No. 02/10575, for example), and one construction is the one shown in FIG. 6 (refer to FIG. 1 of Japanese Unexamined Patent Publication (Kokai) No. 2005-98278, for an example). Incidentally, the heat exchange apparatus for the exhaust gas will be hereinafter called an “EGR module 7”. In FIG. 6, reference numerals the same as in FIG. 2 are used to identify similar constituent members in the EGR module 7 according to the later-appearing first embodiment shown in FIG. 1.

The EGR module 7 shown in FIG. 6 includes a tank 13, an EGR gas cooler 14 arranged inside the tank 13 on the downstream side of the flow of an exhaust gas, that is, on the right side in the drawing, bypass 15 arranged in parallel with the EGR gas cooler 14 and an exhaust gas flow rate ratio regulating valve 18 arranged on the downstream side of the flow of the exhaust gas of the EGR gas cooler 14 and the bypass 15, that is, on the right side in the drawing.

Here, the EGR gas cooler 14 is a heat exchanger for an exhaust gas that conducts heat exchange between an exhaust gas, generated by combustion, and a cooling fluid in order to reduce the generation of nitrogen oxides (NOx) by lowering the EGR gas temperature inside an internal combustion engine.

The EGR gas cooler 14 is mainly constituted by a casing 21, a plurality of exhaust tubes 22 which is accommodated inside the casing 21 and through which the exhaust gas flows, and an inlet side core plate 34 that holds one of the ends of each exhaust tube 22 and separates the inside of the tank 13 from the inside of the casing 21. The periphery of the plurality of exhaust tubes 22 inside the casing 21 is a cooling medium passage 23 through which a cooling fluid such as cooling water flows.

The bypass 15 is pipe that makes the exhaust gas flowing into the EGR module 7 to bypass the EGR gas cooler 14 and allows the exhaust gas to flow out from the EGR module 7. To reduce the number of components, this bypass 15 is inserted into a fitting port for the bypass 15 formed in an inlet side core plate 34 extended to the side of the bypass 15 and is bonded to the inlet side core plate 34.

The exhaust gas exhausted from the internal combustion engine flows into the tank 13 and this tank 13 distributes the flowing exhaust gas into the EGR gas cooler 14 and the bypass 15. The tank 13 has one inlet port 13 a so disposed as to permit the inflow of the exhaust gas and one outlet port 13 j positioned on the opposite side to the inlet port 13 a and so arranged as to exhaust the exhaust gas inside the tank 13. The inlet side core plate 34 is bonded to this outlet port 13 j.

The inlet port 13 a of the tank 13 is so arranged as to oppose both the EGR gas cooler 14 and the bypass 15 and is positioned closer to the EGR gas cooler 14 than to the bypass 15. In other words, the area of the portion 13 h of the opening area of the inlet port 13 a opposing the bypass 15 is smaller than the area of the portion 13 i opposing the EGR gas cooler 14.

This is because the EGR module 7 is mainly directed to cool the exhaust gas and to suppress the pressure loss when the exhaust gas passes through the inside of the EGR gas cooler 14.

In the EGR gas module 7 having such a construction, control by the exhaust gas flow rate ratio regulating valve 18 makes it possible to introduce the exhaust gas into the EGR gas cooler 14 when the combustion temperature is high inside the engine, for example, and to supply the cooled exhaust gas into the engine, and to introduce the exhaust gas into the bypass 15 and to supply the warm exhaust gas into the engine when the combustion temperature inside the engine is low.

Incidentally, the reason why the warm exhaust gas is circulated and supplied into the engine when the combustion temperature inside the engine is low is because HC (hydrocarbons) are likely to occur when the combustion temperature inside the engine is low, such as at the start of the engine, and the generation of HC is suppressed by keeping the combustion temperature at a suitable temperature.

To immediately set the combustion temperature to the suitable temperature, the exhaust gas to be circulated and supplied into the engine preferably has a temperature that is as high as possible. Therefore, when the exhaust gas is not heated by heating means, the heat loss of the exhaust gas flowing through the bypass 15 is preferably small in the EGR module 7 having the construction described above.

Nonetheless, the heat loss of the exhaust gas flowing through the bypass 15 is great in the EGR module 7 having the construction described above for the following reasons.

One of the reasons is as follows. When the exhaust gas is allowed to flow through only the bypass 15, the exhaust gas flowing into the tank 13 strikes the inlet side core plate 34 of the EGR gas cooler 14 as indicated by arrow of dash line in FIG. 6 and then flows inside the bypass 5.

In other words, of the inlet side core plate 34, the portion that constitutes the EGR gas cooler 14 keeps contact with the cooling medium inside the casing 21 and its temperature is low. Therefore, when the exhaust gas strikes the portion of the inlet side core plate 34 constituting the EGR gas cooler 14, the exhaust gas is deprived of its heat by the inlet side core plate 34.

Another reason is as follows. In the EGR module 7 having the construction described above, the bypass 15 is fixed to the inlet side core plate 34 of the EGR gas cooler 14. Therefore, when the exhaust gas passes through the inlet side core plate 34, the heat of the exhaust gas moves to the portion of the inlet side core plate 34 connected to the bypass 15 and further moves to the portion constituting the EGR gas cooler 14 as indicated by a solid line arrow in FIG. 6.

SUMMARY OF THE INVENTION

In view of the problems described above, the present invention aims at providing a heat exchange apparatus for an exhaust gas that can reduce the heat loss from an exhaust gas flowing through a bypass in comparison with a heat exchange apparatus for an exhaust gas according to the prior art.

To accomplish the object described above, the present invention has a feature in that at least the area of the portion of the inlet port (13 a) in the tank (13) opposing the bypass (15) is greater than the area of the portion of the inlet port (13 a) opposing the exhaust gas heat exchanger (14).

Consequently, when the exhaust gas is caused to flow through the bypass, the exhaust gas flowing from the inlet port of the tank is allowed to more easily flow into the bypass and the amount of the exhaust gas striking the low temperature portion of the core plate, etc, can be decreased to reduce the heat loss from the exhaust gas in comparison with the heat exchange apparatus for the exhaust gas according to the prior art shown in FIG. 6.

Incidentally, the term “position at which at least the area of the portion of the inlet port (13 a) in the tank (13) opposing the bypass (15) is greater than the area of the portion of the inlet port (13 a) opposing the exhaust gas heat exchanger (14)” includes also the position at which the inlet port (13 a) does not oppose the exhaust gas heat exchanger (14) but opposes only the bypass (15) of the exhaust gas heat exchanger (14) and the bypass (15).

The position of the inlet port of the tank described above can be the position at which the inlet port opposes only the bypass (15) of the exhaust gas heat exchanger (14) and the bypass (15), for example, as in the present invention.

When the inlet port of the tank is arranged at the position at which it opposes only the bypass in this way, the main stream of the exhaust gas does not strike the low temperature portions such as the core plate constituting the exhaust gas heat exchanger when the exhaust gas is allowed to flow through the bypass, and the exhaust gas can be guided from the inlet port of the tank to the bypass.

In consequence, the heat loss of the exhaust gas can be reduced in comparison with the heat exchange apparatus for the exhaust gas according to the prior art in which the inlet port is arranged at the position at which it opposes either wholly or partially the exhaust gas heat exchanger.

In such a case, the heat loss of the exhaust gas when the exhaust gas is caused to flow through the bypass can be reduced much more when the distance between the inlet port of the tank and the exhaust gas heat exchanger becomes greater in a planar direction when the inlet port of the tank, the bypass and the exhaust gas heat exchanger are projected on the same plane in the longitudinal direction, but the pressure loss of the gas occurring when the exhaust gas is allowed to flow through the exhaust gas heat exchanger becomes greater.

Therefore, the position of the inlet port of the tank can be set to the position at which the open end (13 e) of the inlet port (13 a) positioned on the side of the exhaust gas heat exchanger (14) and the open end (15 b) of the bypass (15) positioned on the side of the exhaust gas heat exchanger (14) oppose each other.

Consequently, when the inlet port of the tank is arranged at the position at which it opposes only the bypass, the pressure loss of the gas that occurs when the exhaust gas is caused to flow through the exhaust gas heat exchanger can be reduced to minimum.

Incidentally, the term “open end (13 e) of the inlet port (13) and the open end (15 b) of the bypass (15) oppose each other” means that when the inlet port of the tank and the bypass are projected on the same plane, the open end (13 e) of the inlet port (13 a) and the open end (15 b) of the bypass (15) overlap with each other.

Another feature of the present invention resides in that the tank (13) has a first outlet port (13 b) and a second outlet port (13 c). Here, the first outlet port (13 b) is an outlet port to which the exhaust gas heat exchanger (14) is connected and which guides the exhaust gas inside the tank (13) to the exhaust gas heat exchanger (14). On the other hand, the second outlet port (13 c) is an outlet port which is arranged in the spaced-apart relation from the first outlet port (13 b), to which the bypass (15) is connected and which guides the exhaust gas inside the tank (13) to the bypass (15).

As described above, the first outlet port (13 b) connected to the exhaust gas heat exchanger (14) and the second outlet port (13 c) connected to the bypass (15) are separately provided to the tank in this invention. Therefore, the bypass can be fixed to the tank without relying on the core plate constituting the exhaust gas heat exchanger.

As a result, the present invention can suppress heat migration from the bypass to the core plate and can reduce the heat loss of the exhaust gas flowing through the bypass in comparison with the exhaust gas heat exchange apparatus according to the prior art in which the bypass is fixed to the core plate.

Incidentally, the reference numerals in parentheses, to denote the above means, are intended to show the relationship of the specific means which will be described later in an embodiment of the invention.

The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an overall construction of an exhaust gas recirculation apparatus for a diesel engine;

FIG. 2 is a partial sectional view of an EGR module 7 in FIG. 1 in the first embodiment of the present invention;

FIG. 3 is a side view showing a part of an EGR module 7 in FIG. 1 in the second embodiment of the present invention;

FIG. 4 is a side view showing a part of an EGR module 7 in FIG. 1 in one example of another embodiment of the present invention;

FIG. 5 is a partial sectional view showing a part of an EGR module 7 in FIG. 1 in a second example of another embodiment of the present invention;

FIG. 6 is a partial sectional view showing an EGR module 7 in FIG. 1 according to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To begin with, the first embodiment of the invention will be explained. In this embodiment, an example where the invention is applied to an EGR module 7, as an exhaust gas heat exchange apparatus used in an exhaust gas recirculation apparatus for an internal combustion engine, will be explained.

FIG. 1 shows an overall construction of an exhaust gas recirculation apparatus for an internal combustion engine that uses the EGR module 7 according to the first embodiment. The exhaust gas recirculation apparatus for an internal combustion engine shown in FIG. 1 is used for a diesel engine, as an internal combustion engine, for example.

The exhaust gas recirculation apparatus for an internal combustion engine includes an exhaust tube 2 through which an exhaust gas of the engine 1 flows and an exhaust gas recirculation circuit 4 connected to an intake tube 3 through which intake air filtered by an air cleaner flows.

The exhaust gas recirculation circuit 4 is for recirculating a part of the exhaust gas flowing through the exhaust tube 2 into the intake tube 3. The exhaust gas so recirculated is the EGR gas. The exhaust gas recirculation circuit 4 includes an exhaust side exhaust gas recirculation tube 5 branching from the exhaust tube 2, an intake side exhaust gas recirculation tube 6 that is confluent with the intake tube 3, and an EGR module 7 directly connected between the exhaust side exhaust gas recirculation tube 5 and the intake side exhaust gas recirculation tube 6.

An engine cooling water circuit for circulating and supplying engine cooling water to the EGR module 7 is provided to the engine 1. The engine cooling water circuit includes a cooling water pipe 8 for circulating and supplying cooling water from a water jacket, not shown, of the engine 1 to a cooling water inlet pipe 11 of the later-appearing EGR module 7, a cooling water pipe 9 for circulating and supplying engine cooling water from a cooling water outlet pipe 12 of the EGR module 7 to the water jacket of the engine 1 through a radiator not shown, and a water pump for generating a circulating flow of cooling water inside the engine cooling water circuit.

As will be described later, the EGR module 7 includes an EGR gas cooler 14, a bypass 15, an exhaust gas flow rate ratio regulating valve 18 and an exhaust gas flow rate controlling valve 19.

Next, the construction of the EGR module 7 will be concretely explained. FIG. 2 shows a partial sectional view of the EGR module 7 according to this embodiment. Incidentally, an up-down direction of FIG. 2 corresponds to a vertical direction and the EGR module 7 is mounted to a car in the state shown in FIG. 2.

The EGR module 7 of this embodiment is different from the EGR module 7 of the prior art shown in FIG. 6 mainly with regard to the shape of a tank 13 and a fixing method of a bypass 15, but other structural portions are the same as those of the EGR module 7 of the prior art shown in FIG. 6. Incidentally, the EGR module 7 shown in FIG. 6 is described in Patent Document 2. Therefore, the explanation will be given mainly on the different portions from the EGR module 7 shown in FIG. 6 and explanations of the portions similar to those of the EGR module 7 in FIG. 6 will be partly omitted.

In the same way as does the EGR module 7 of the prior art shown in FIG. 6, the EGR module 7 of this embodiment includes a tank 13, an EGR gas cooler 14 as an exhaust gas heat exchanger arranged on the downstream side of the flow of the exhaust gas of the tank 13, a bypass 15 arranged in parallel with the EGR gas cooler 14, a connection joining portion 16 arranged on the downstream side of the flow of the exhaust gas of the EGR gas cooler 14 and the bypass 15, a valve housing 17 connected to the EGR gas cooler 14 and to the bypass 15 through the connection joining portion 16, and an exhaust gas flow rate ratio regulating valve 18 and an exhaust gas flow rate controlling valve 19 accommodated inside the valve housing 17.

The EGR gas cooler 14 conducts heat exchange between the high temperature EGR gas introduced from the exhaust gas recirculation circuit 4 with low temperature engine cooling water flowing from the cooling water passage formed inside the cooling water pipe 8 and cools the EGR gas to a desired exhaust gas temperature.

The EGR gas cooler 14 includes a casing 21, a plurality of exhaust tubes 22, an inlet side core plate 34 and an outlet side core plate 35. The casing 21 constitutes a cooling water passage 23 through which engine cooling water circulates around a plurality of exhaust tubes 22.

A tank 13 is integrally connected to one of the ends of the casing 21 in the longitudinal direction and the valve housing 17 is integrally connected through the connection joining portion 16 to the other end of the casing 21 in the longitudinal direction. Consequently, the EGR gas flowing into the tank 13 flows from the side of the tank 13 to the valve housing 17 inside a plurality of exhaust tubes 22.

A cooling water inlet pipe 11 for allowing engine cooling water to flow from a water jacket of the engine 1 into a cooling water passage 23 and a cooling water outlet tube 24 for guiding engine cooling water from the cooling water passage 23 into the valve housing 17 through the connection joining portion 16 are provided in the casing 21.

In this embodiment, the cooling water inlet pipe 11 is arranged on the tank 13 side and engine cooling water is allowed to flow inside the casing 21 as the cooling water passage 23 in the same direction as the EGR gas flowing inside a plurality of exhaust tubes 22.

The casing 21 is formed of a metal material having high heat resistance and high corrosion resistance such as stainless steel and has a prismatic shape, for example. Incidentally, a plurality of reinforcing ribs 25 are equidistantly formed in such a fashion as to describe a protrusive shape towards the outside for improving the pressure resistance.

The plural exhaust tubes 22 are formed of a metal material having high heat resistance and high corrosion resistance such as stainless steel in the same way as the casing 21. The exhaust tubes 22 are shaped into a flat tubular shape, for example, and a first exhaust gas passage 31 through which the EGR gas flows is formed inside each exhaust tube. A plurality of exhaust tubes 22 is stacked in the direction of a minor diameter with predetermined gaps among them and the direction of the major diameter is so extended as to cover the full length of the cylindrical direction of the casing 21.

To increase the heat transfer area with the EGR gas and to improve heat exchange efficiency between the EGR gas and engine cooling water, inner fins (not shown) of a rectangular wave shape, for example, are arranged inside a plurality of exhaust tubes 22.

The plurality of exhaust tubes 22 is integrally bonded to the inlet side core plate 34 by brazing or welding, on the tank 13 side in the state where one of the end of each exhaust tube 22 is fitted into each of insertion holes formed in the inlet side core plate 34. One of the ends of the tank 13 side of the casing 21 is integrally bonded to this inlet side core plate 34.

On the side of the tank 13 of the casing 21 and the plurality of exhaust tubes 22, the casing 21, the inlet side core plate 34, and the tank 13 are integrally bonded in the state where the inlet side core plate 34 is interposed between one of the ends of the tank 13 of the casing 21 and the tank 13. Incidentally, the inlet side core plate 34 of this embodiment is not connected to the bypass 15.

The plurality of exhaust tubes 22 is integrally bonded to the outlet side core plate 35 by brazing or welding, on the valve housing 17 side, in the state where one of the end of each exhaust tube 22 on the valve housing side 17 is fitted into each of insertion holes formed in the outlet side core plate 35.

On the side of the valve housing 17 of the casing 21 and the plurality of exhaust tubes 22, one of the ends of each of the outlet side core plate 35 and one of the ends of the casing 21 on the valve housing side 17 are integrally bonded to the connection joining portion 16.

The bypass 15 is arranged between the tank 13 and the connection joining portion 16 and is substantially the same size as the size of the casing 21 of the EGR gas cooler 14 in the cylindrical direction, in parallel with the EGR gas cooler 14 and in the proximity of the EGR gas cooler 14. The bypass 15 is arranged, for example, below the EGR gas cooler 14 in the vertical direction.

The bypass 15 is formed of a metal material excellent in heat resistance and corrosion resistance such as the stainless steel in the same way as the casing 21. The bypass 15 is shaped into a round cylindrical tube, for example, and a second exhaust gas passage 32 through which the EGR gas flows is formed inside the bypass 15.

The end portion of the bypass 15 on the tank 13 side in the longitudinal direction is directly connected to the tank 13 and its end portion on the valve housing side 17 in the longitudinal direction is directly connected to the connection joining portion 16. A bellows portion 36 capable of extending and contracting in the cylindrical direction of the bypass 15 is integrally formed with the bypass 15.

The inside of the tank 13 is a space for guiding the EGR gas introduced from the exhaust side exhaust gas recirculation tube 5 to either one, or both, of the EGR cooler 14 and the bypass 15.

The tank 13 is constituted by a tank plate 33. The tank 13 has therein one inlet port 13 a formed in the tank plate 33 so as to guide the EGR gas from the exhaust side exhaust gas recirculation tube 5 and two outlet ports 13 b and 13 c formed in the tank plate 33 so as to guide the EGR gas inside the tank 13 into the EGR gas cooler 14 or into the bypass 15. The EGR gas passes through these inlet hole 13 a and outlet holes 13 b and 13 c.

Here, the tank plate 33 is formed of a metal material excellent in heat resistance and corrosion resistance, such as the stainless steel, in the same way as is the casing 21.

The two outlet ports 13 b and 13 c are positioned on the opposite side to the inlet port 13 a in the tank 13. The two outlet ports 13 b and 13 c are arranged at upper and lower positions in the spaced-apart relation in the vertical direction. Incidentally, of the two outlet ports, the outlet port 13 b arranged at the upper position will be called “upper outlet port” and the outlet port at the lower position, “lower outlet port”. The upper outlet port 13 b and the lower outlet port 13 c correspond to a first outlet port and a second outlet port, as described in the Scope of Claim for Patent, respectively.

The opening shape of the upper outlet port 13 b corresponds to the opening shape at the end of the casing 21 on the tank 13 side in the EGR gas cooler 14. The end portion of the casing 21 on the tank 13 side is connected by brazing or welding to the upper outlet port 13 b of the tank 13 through the core plate 34.

On the other hand, the opening shape of the lower outlet port 13 c corresponds to the opening shape at the end of the bypass 15 on the tank 13 side. The end portion of the pipe 15 on the tank 13 side is directly connected by brazing or welding to the lower outlet port 13 c of the tank 13. Incidentally, the bypass 15 can be connected indirectly to the lower outlet port 13 c of the tank 13 through the connection portion, though this construction is not shown in the drawing.

The inlet port 13 a is arranged at a position deviated towards the down side in FIG. 2, that is, towards the bypass 15, in comparison with the inlet port 13 a of the tank 13 shown in FIG. 6. More concretely, the inlet port 13 a is arranged at the position opposing only the lower outlet port 13 c of the upper and lower outlet ports 13 b and 13 c with respect to the tank 13 as shown in FIG. 2. In other words, the inlet port 13 a is arranged at the position opposing only the bypass 15, among the EGR cooler 14 and the bypass 15, in the tank 13.

In this embodiment, in particular, the opening shape of the inlet port 13 a of the tank 13 and the opening shape of the bypass 15 on the tank 13 side are equivalent to each other. In other words, the opening diameter 13 d of the inlet port 13 a of the tank 13 is equal to the opening diameter 15 a of the bypass 15 on the tank 13 side.

The position of the open upper end 13 e of the inlet port 13 a of the tank 13 is coincident with the position of the open upper end 15 b of the bypass 15 in the vertical direction, and the position of the open lower end 13 f of the inlet port 13 a of the tank 13 is coincident with the position of the open lower end 15 c of the bypass 15.

In this way, the inlet 13 a of the tank 13 completely opposes the second exhaust gas passage 32 constituted inside the bypass 15. Incidentally, a flange 13 g that is to be connected and fixed to the exhaust side exhaust gas recirculation tube 5 is disposed on the inlet side of the tank 13 and the inlet port 13 a is disposed on the center side.

The connection joining portion 16 directly couples, in series, the downstream side of the EGR gas cooler 14 and the bypass 15 to the valve housing 17. The connection joining portion 16 is formed of a metal material excellent in heat resistance and corrosion resistance, such as stainless steel, in the same way as the casing 21.

The connection joining portion 16 has on its outer peripheral side a fitting flange portion 37 for direct coupling with the valve housing 17. The connection joining portion 16 has on its inner peripheral side a side wall portion 38 on the EGR gas cooler 14 side, a side wall portion 39 on the bypass 15 side and a connection portion 40 positioned between the side wall portion 38 on the EGR gas cooler 14 side and the side wall portion 39 on the bypass side 15, for connecting these side wall portions. Incidentally, the thickness of the connection portion 40 in the longitudinal direction of the EGR gas cooler 14, that is, the thickness in the horizontal direction, is smaller than that of the flange portion 37.

An outlet side core plate 35 of the EGR gas cooler 14 is integrally connected to the side wall portion 38 on the EGR gas cooler 14 side and one of the ends of the casing 21 of the EGR gas cooler 14 is integrally connected to the flange portion 37.

A space is defined between the side wall portion 38 on the EGR gas cooler 14 side and the flange portion 37 above the side wall portion 38 on the EGR gas cooler 14 side inside the connection joining portion 16. This space is positioned at the upper end of the portion of the outlet side core plate 35 into which a plurality of exhaust tubes 22 is inserted, and the extension portion 35 a of the outlet side core plate 35 extending in the longitudinal direction of the EGR gas cooler 14 divides this space into the cooling water passage 26 through which cooling water flows and the first exhaust gas passage 31 b through which the EGR gas flows.

The cooling water passage 26 inside the connection joining portion 16 directly communicates the cooling water outlet portion 24 of the cooling passage 23 of the casing 21 with the cooling water passage 27 inside the valve housing 17 to be later described. The first exhaust gas passage 31 b inside the connection joining portion 16 communicates with a plurality of exhaust tubes 22.

The bypass 15 is integrally bonded by brazing or welding to the side wall portion 39 and the flange portion 37 on the side of the bypass 15. These side wall portion 39 and flange portion 37 on the side of the bypass 15 constitute therein the second exhaust gas passage 32 b through which the EGR gas from the bypass 15 flows.

The exhaust gas flow rate ratio regulating valve 18 and the exhaust gas recirculation rate controlling valve 19 are integrally fitted to the valve housing 17.

Inside the valve housing 17 are formed a first exhaust gas introduction passage 41, a second exhaust gas introduction passage 42, an exhaust gas recirculation circuit 43, a communication passage 45 communicating with this exhaust gas recirculation circuit 43 and an exhaust gas recirculation circuit 46 for introducing the EGR gas from this communication passage 45 into the exhaust gas recirculation circuit 4 formed inside the intake side exhaust gas recirculation tube 6.

Here, the first exhaust gas introduction passage 41 is constituted in such a fashion that the EGR gas can be introduced from the first exhaust gas passage 31 of the EGR gas cooler 14 through the first exhaust gas passage 31 b. The second exhaust gas introduction passage 42 is constituted in such a fashion that the EGR gas can be introduced from the second exhaust gas passage 31 of the bypass 15 through the second exhaust gas passage 32 b.

The exhaust gas recirculation circuit 43 is constituted in such a fashion that the EGR gas can be introduced from the first exhaust gas introduction passage 41 through the first introduction port 51 and from the second exhaust gas introduction passage 42 through the second introduction port 52.

The communication passage 45 constitutes a valve port of the exhaust gas recirculation rate controlling valve 19 that communicates with the first exhaust gas passage 31 of the EGR gas cooler 14 through the first exhaust gas introduction passage 41 and the first introduction port 51 and communicates with the exhaust gas passage 32 through the second exhaust introduction passage 42 and the second introduction port 52.

These first exhaust gas introduction passage 41, second exhaust gas introduction passage 42, exhaust gas recirculation circuit 43, communication passage 45 and exhaust gas recirculation circuit 46 constitute the exhaust gas recirculation circuit 4.

Inside the valve housing 17 is formed the cooling water passage 27 into which engine cooling water is introduced from the cooling water outlet portion of the cooling water passage 23 of the EGR gas cooler 14 through the cooling water passage 26. This cooling water passage 27 is for cooling the valve housing 17. Incidentally, the cooling water inlet portion 27 a disposed at the extreme left of the cooling water passage 27 in the drawing is directly coupled in series with the cooling water passage 26 of the connection joining portion 16. A cooling water outlet pipe 12 connected to the cooling water pipe 9 is disposed at the extreme left of the cooling water passage 27 in the drawing.

The valve housing 17 is integrally molded, into a predetermined shape, as an aluminum casting or an aluminum die casting and is fixed to the downstream portion of the connection joining portion 16 by using a screw or a fastening bolt not shown in the drawing. Known measures are employed for the connection portion between the valve housing 17 and the connection joining portion 16 lest engine cooling water and the EGR gas leak.

When a metal material capable of being integrally brazed to the connection joining portion 16 is used as the material of the valve housing 17, the valve housing 17 can be brazed, too, when the EGR module 7 is integrally molded. The valve housing 17 and the connection joining portion 16 can be bonded by welding, too.

The exhaust gas flow rate regulating valve 18 continuously regulates the ratio of the flow rate of the EGR gas flowing inside each first exhaust gas passage 31 of the EGR gas cooler 14 to the flow rate of the EGR gas flowing inside the second exhaust gas passage 32 of the bypass 14.

The exhaust gas flow rate ratio regulating valve 18 includes a metallic double poppet valve 53 for regulating the opening areas of first and second introduction ports 51 and 52 disposed inside the valve housing 17, a metallic valve shaft 54 reciprocating integrally with the double poppet valve 53 in the axial direction, a negative pressure operation type actuator as valve body driving means for driving the double poppet valve 53 and the valve shaft 54 upward in the drawing and valve body urging means for urging downward the double poppet valve 53 and the valve shaft 54 in the drawing.

Here, the double poppet valve 53 includes a first valve body 61 for regulating an opening area of the first introduction port 51, a second valve body 62 for regulating an opening area of the second introduction port 52 and a cylindrical connection portion 63 for connecting the first and second valve bodies 61 and 62. The double poppet valve 53 is formed of a metal material excellent in heat resistance and corrosion resistance, such as stainless steel, and is shaped into a substantially disk-like shape, for example.

The valve shaft 54 is disposed in a bearing 57 that is accommodated and held, inside a bearing support portion of the valve housing 17 on the left side in the drawing, in such a fashion as to be capable of sliding, and is formed of a metal material excellent in heat resistance and corrosion resistance, such as stainless steel, in the same way as the double poppet valve 53. The double poppet valve 53 is held and fixed to a valve holding portion of the valve shaft 54 by fixing means such as welding.

The negative pressure operation actuator allows the double poppet valve 53 as well as the valve shaft 54 to undergo reciprocation and displacement in the axial direction by controlling a pressure difference between a negative pressure chamber 65 a defined between a casing 60 and a thin membrane-like diagram 64 and an atmospheric pressure chamber 65 b, by an electromagnetic or electric negative pressure valve, to cause displacement of the diaphragm 64.

The exhaust gas recirculation controlling valve 19 continuously regulates the total flow rate of the EGR gas passing through the valve housing 17.

The exhaust gas recirculation flow rate controlling valve 19 includes a metallic valve 71 for regulating an opening area of a communication passage 45 formed inside the valve housing 17, a metallic valve shaft 72 operating integrally with this valve 71 in a rotating direction, valve driving means, not shown, for driving the valve 71 and the valve shaft 72 in the valve opening direction and urging means, not shown, for urging the valve 71 and the valve shaft 72 in a valve closing direction.

The valve 71 is formed of a metal material excellent in heat resistance and corrosion resistance, such as stainless steel, and is shaped into a substantially disk-like shape, for example. The valve shaft 72 is formed of a metal material excellent in heat resistance and corrosion resistance, such as stainless steel, in the same way as the valve 71. The valve 71 is held and fixed to a holding portion of the valve shaft 72 by fixing means such as welding.

The valve body driving means of the exhaust gas recirculation rate controlling valve 19 drives the valve 71 in the valve opening direction by rotating and driving the valve shaft 72 by an electric actuator constituted by a power unit.

The power unit includes a driving motor, not shown in the drawing, for driving the valve 71 and the valve shaft 72 of the exhaust gas recirculation rate controlling valve 19 in the rotating direction and a power transmission mechanism, not shown, for transmitting the turning power of the driving motor to the valve shaft 72 of the exhaust gas recirculation rate controlling valve 19.

Next, the operation of the EGR module 7 of this embodiment will be explained.

The EGR gas flows into the intake tube 3 from the exhaust tube 2 through the exhaust gas recirculation circuit 4, the EGR module 7 and the intake side exhaust gas recirculation tube 6 as indicated by an arrow in FIG. 1.

At this time, the valve 71 of the exhaust gas recirculation rate controlling valve 19 is driven by the valve body driving means through the valve shaft 72 and the opening area of the communication passage 45 is adjusted. Consequently, the total flow rate of the EGR gas passing through the exhaust gas recirculation circuit 43 of the valve housing 17, the communication passage 45 and the exhaust gas recirculation circuit 46, that is, the total flow rate of the EGR gas to be circulated and supplied to the intake tube 3, is regulated.

As the double poppet valve 52 of the exhaust gas flow rate regulating valve 18 is driven by the valve body driving means, the opening areas of the first and second introduction holes 51 and 52 are adjusted.

In other words, when the valve shaft 54 is driven upward in the drawing by the valve body driving means, the first valve body 61 on the side of the EGR gas cooler 14 moves in the valve closing direction and at the same time, the second valve body 62 on the side of the bypass 15 moves in the valve opening direction.

On the contrary, when the valve shaft 54 is not driven by the valve body driving means, the valve shaft 54 moves downward in the drawing owing to the valve body urging means 55, so that the first valve body 61 on the side of the EGR gas cooler 14 moves in the valve opening direction and at the same time, the second valve body 62 on the side of the bypass 15 moves in the valve closing direction.

In this way, the double poppet valve 53 regulates the opening areas of the first and second introduction ports 51 and 52. Consequently, the ratio of the flow rate of the EGR gas flowing inside each first exhaust gas passage 31 of the EGR gas cooler 14 to the flow rate of the EGR gas flowing inside the second exhaust gas passage 32 of the bypass 15 is regulated.

When the combustion temperature inside the engine is high, for example, the first valve body 61 on the side of the EGR gas cooler 14 is opened while the second valve body 62 on the side of the bypass 15 is closed. Consequently, regarding the EGR gas cooler 14 and the bypass 15, the EGR gas is allowed to flow only through each first exhaust gas passage 31 of the EGR gas cooler 14 and the EGR gas cooled by engine cooling water can be circulated and supplied to the intake tube 3 of the engine 1.

When the combustion temperature inside the engine is low, on the other hand, the first valve body 61 on the side of the EGR gas cooler 14 is closed while the second valve body 62 on the side of the bypass 15 is opened. Consequently, regarding the EGR gas cooler 14 and the bypass 15, the EGR gas is allowed to flow only through the second exhaust gas passage 32 of the bypass 15 and the EGR gas having a high temperature can be circulated and supplied as such to the intake tube 3 of the engine 1.

Incidentally, the temperature of the EGR gas can be adjusted by opening both of the first and second valve bodies 61 and 62 and adjusting both of the opening degrees.

Engine cooling water for cooling the EGR gas inside the EGR gas cooler 14 flows inside the cooling water pipe 8 from the water jacket of the engine 1, not shown, flows into the cooling water passage 23 of the EGR gas cooler 14 through the cooling water inlet pipe 11, takes away the heat of the EGR gas flowing inside the first exhaust gas passage 31 of the EGR gas cooler 14 and cools the EGR gas.

Subsequently, engine cooling water flows from the cooling water outlet portion of the cooling water passage 23 of the EGR gas cooler 14 into the cooling water passage 26 of the connection joining portion 16. Engine cooling water flowing into the cooling water passage 26 flows into the cooling water passage 27 of the housing 17 and cools the valve housing 17 heated to a high temperature by the heat of the EGR gas. Engine cooling water is thereafter circulated and supplied to the water jacket of the engine 1 from the cooling water outlet pipe 12 of the EGR module 7 through the radiator.

Next, the main effects of the EGR module 7 according to this embodiment will be explained.

(1) The inlet port 13 a disposed in the tank 13 in this embodiment is arranged at a position opposing only the bypass 15 among the EGR gas cooler 14 and the bypass 15 in the tank 13.

When the EGR gas is caused to flow only through the second exhaust gas passage 32 of the bypass 15 of the EGR gas cooler 14 and the bypass 15 in the EGR module 7, the EGR gas flows into the tank 13 from the exhaust tube 2 through the exhaust side exhaust gas recirculation tube 5 and flows through the second exhaust gas passage 32 of the bypass 14 from the lower outlet port 13 c of the tank 13.

According to the EGR module 7 of this embodiment, at this time, the main stream of the exhaust gas flowing into the tank 13 from the inlet port 13 a as indicated by arrow of broken line in FIG. 2 can be guided to the bypass 15 without striking the inlet side core plate 34 constituting the EGR gas cooler 14.

As shown in FIG. 6, therefore, the heat loss resulting from the impingement of the EGR gas against the inlet side core plate 34 constituting the EGR gas cooler 14 can be reduced in comparison with a heat exchanger for an exhaust gas in which a part of the inlet port 13 a is arranged at a position opposing the EGR gas cooler 14 and a heat exchanger for an exhaust gas according to the prior art in which the inlet port 13 a is fully arranged at a position opposing the EGR gas cooler 14.

In this embodiment, in particular, the inlet port 13 a of the tank 13 completely opposes the second exhaust gas passage 32 formed inside the bypass 15. In other words, the opening shape of the inlet port 13 a of the tank 13 and the shape of the second exhaust gas passage 32 formed inside the bypass 15 are similar and their positions in the vertical direction are coincident.

Therefore, the portion ranging from the inlet port 13 a of the tank 13 to the second exhaust gas passage 32 of the bypass 15 can be regarded as one tube having a uniform inner diameter. In comparison with the case where the inlet port 13 a does not completely oppose the second exhaust gas passage 32 of the bypass 15, the pressure loss in the EGR gas when the EGR gas flows from the inlet port 13 a of the tank 13 to the second exhaust gas passage 32 of the bypass 15 can be reduced.

Incidentally, when the EGR gas is caused to flow only through each first exhaust gas passage 31 of the EGR gas cooler 14, the second introduction port 52 is closed by the double poppet valve 53 of the exhaust gas flow rate ratio regulating valve 18. Consequently, even when the inlet port 13 a is arranged at the position opposing only the bypass 15, the EGR gas flowing into the tank 13 can be caused to flow into each first exhaust gas passage 31 of the EGR gas cooler 14 from the upper outlet port 13 b of the tank 13.

(2) In this embodiment, the position of the open upper end 13 e of the inlet port 13 a of the tank 13 is coincident with the position of the open upper end 15 b of the bypass 15 in the vertical direction.

From the aspect of reducing the heat loss of the EGR gas when the EGR gas is caused to flow through only the second exhaust gas passage 32 of the bypass 15, it is preferred to arrange the open upper end 13 e of the inlet port 13 a of the tank 13 as close as possible to the down position of the tank 13 in the vertical direction because, when the open upper end 13 e of the inlet port 13 a of the tank 13 is arranged at the position as lower as possible than the inlet side core plate 34 of the EGR gas cooler 14, it becomes more difficult for the EGR gas to impinge against the inlet side core plate 34.

However, when the open upper end 13 e of the inlet port 13 a of the tank 13 is arranged below the inlet side core plate 34, the pressure loss of the EGR gas when the EGR gas is caused to flow through the EGR gas cooler becomes greater when the position of the open upper end 13 e is deviated downward.

Therefore, the position of the open upper end of the inlet port 13 a of the tank 13 is preferably coincident with the position of the open upper end 15 b of the bypass 15 in the vertical direction as in this embodiment.

Consequently, when the EGR gas is caused to flow only through the bypass 15, the main stream of the EGR gas can be allowed to flow through the bypass 15. On the other hand, when the EGR gas is caused to flow only through the EGR gas cooler 14, the pressure loss of the EGR gas when the EGR gas flows from the inside of the tank 13 through the inside of the EGR gas cooler 14 can be made smaller than when the open upper end 13 e of the inlet port 13 a of the tank 13 is positioned below the open upper end 15 b of the bypass 15.

As a result, it becomes possible to simultaneously reduce the heat loss of the EGR gas when it is caused to flow only through the second exhaust gas passage 32 of the bypass 15 and to suppress the pressure loss of the EGR gas when the EGR gas is caused to flow through the EGR gas cooler 14.

(3) In this embodiment, the tank 13 has two outlet ports 13 b and 13 c that are arranged at upper and lower positions in the vertical direction in the spaced-apart relation. Of these two outlet ports 13 b and 13 c, the casing 21 of the EGR gas cooler 14 is connected to the upper outlet port 13 b through the inlet side core plate 34 and the bypass 15 is connected to the lower outlet port 13 c without passing through the inlet side core plate 34.

As the upper outlet port 13 b connected to the EGR gas cooler 14 and the lower outlet port 13 c connected to the bypass 15 are separately provided to the tank 13 as described above, the bypass 15 can be connected to the tank 13 without passing through the inlet side core plate 34.

As the upper outlet port 13 b and the lower outlet port 13 c are spaced apart from each other, heat migration from the bypass 15 to the inlet side core plate 34 of the EGR gas cooler 14 can be routed to the tank 13. In other words, the movement of heat of the bypass 15 to the inlet side core plate 34 of the EGR gas cooler 14 becomes more difficult than in the EGR module 7 shown in FIG. 6.

Accordingly, in comparison with the exhaust gas heat exchange apparatus of the prior art in which the bypass 15 is fixed to the inlet side core plate 34, the heat movement from the bypass 15 to the inlet side core plate 34 can be suppressed and the heat loss of the EGR gas flowing inside the bypass 15 can be reduced.

(4) As to the connection of the EGR gas cooler 14 and the bypass 15 with the connection joining portion 16 in this embodiment, the outlet side core plate 35 of the EGR gas cooler 14 is integrally connected to the side wall portion 38 on the side of the EGR gas cooler 14 positioned on the inner peripheral side of the connection joining portion 16, and the bypass 15 is integrally connected to the side wall portion 39 on the side of the bypass 15.

The side wall portion 38 of the connection joining portion 16 on the side of the EGR gas cooler 14 and the side wall portion 39 on the side of the bypass 15 have a continuous shape through the connection portion 40.

Consequently, when the heat moves from the bypass 15 to the outlet side core plate 35 of the EGR gas cooler 14 through the connection joining portion 16, the heat of the bypass 15 transfers to the side wall portion 39 on the side of the bypass 15, bypasses the connection portion 40, transfers to the side wall portion 38 on the side of the EGR gas cooler 14 and then moves to the outlet side core plate 35 of the EGR gas cooler 14.

In comparison with the EGR module 7 of the prior art shown in FIG. 6, therefore, this embodiment can make the heat movement from the bypass 15 to the outlet side core plate 35 of the EGR gas cooler 14 more difficult. As a result, the heat loss of the EGR gas flowing through the bypass 15 can be reduced.

Next, the second embodiment will be explained. FIG. 3 shows a part of the EGR module 7 in the second embodiment. FIG. 3 is a view corresponding to the portion near the tank 13 in FIG. 2. Incidentally, like reference numerals are used in FIG. 3 to identify like constituent members in the EGR module 7 shown in FIG. 2.

The first embodiment was explained with respect to the EGR module 7 having the construction in which the bypass 15 is arranged outside the casing 21 of the EGR gas cooler 14 by way of example but the bypass 15 can be arranged inside the casing 81 of the EGR gas cooler 14 as in this embodiment.

As shown in FIG. 3, the EGR module 7 according to this embodiment includes an integral casing 81 of the EGR gas cooler 14 and the bypass 15 and a separator 82 in place of the casing 21 of the EGR gas cooler 14 shown in FIG. 2. Incidentally, the constructions of the tank 13 and other members are the same as those of the EGR module 7 shown in FIG. 2.

The integral casing 81 has a rectangular cylindrical shape, for example. The separator 82 is arranged inside the casing 81 and divides the inside of the casing 81 into two areas.

Of these two areas, one of the areas, on the upper side of the drawing above the separator 82, is the area for the EGR gas cooler 14. A plurality of exhaust tubes 22 is arranged in this area, though not shown in the drawing, in the same way as the EGR module 7 shown in FIG. 2. In this way, the casing 81 and the separator 82 constitute the outer wall of the EGR gas cooler 14 in this embodiment.

The casing 81 and the separator 82 constituting the outer wall of the EGR gas cooler 14 are integrally connected to the upper outlet hole 13 b of the tank 13 through the inlet side core plate 34 so that the upper area above the separator 82 inside the casing 81 communicates with the inside of the tank 13. The casing 81 and the separator 82 are formed of a metal material excellent in heat resistance and corrosion resistance such as stainless steel.

On the other hand, the bypass 15 is arranged in the other area, that is, the lower area, below the separator 82 and inside the casing 81. The bypass 15 is similar to the bypass 15 shown in FIG. 2 and is integrally connected to the lower outlet hole 13 c of the tank through the inlet portion 15 d. Incidentally, this inlet portion 15 d is integral with the casing 81 and the bypass 15.

In this embodiment, too, the inlet hole 13 a disposed in the tank 13 is arranged at the position opposing only the bypass 15 among the EGR gas cooler 14 and the bypass 14 in the tank 13 in the same way as in the first embodiment. The position of the open upper end of the inlet hole 13 a of the tank 13 is coincident with the position of the open upper end 15 b of the bypass 15 in the vertical direction.

Therefore, this embodiment has the effects (1) and (2) explained in the first embodiment.

Incidentally, this embodiment has been explained in the case where the bypass 15 is arranged inside the casing 81 of the EGR gas cooler 14 by way of example but the EGR gas cooler 14 and the bypass 15 can be constituted inside the casing 81 by merely partitioning the inside of the EGR gas cooler 14 by a separator.

Finally, other embodiments will be explained.

(1) Each of the foregoing embodiments has been explained in the case, by way of example, where the inlet port 13 a of the tank 13 opposes only the bypass 15 and the open upper end 13 e of the inlet port 13 a of the tank 13 is coincident with the open upper end 15 b of the bypass 15 in the vertical direction. However, the open upper end 13 e of the inlet port 13 a of the tank 13 may be positioned below the open upper end 1 b of the bypass tank 15 in the vertical direction.

In consequence, as the position of the inlet port 13 a of the tank 13 is spaced apart from the EGR gas cooler 14 in the vertical direction, it is more hard for the EGR gas to impinge against the inlet side core plate 34 than in the first and second embodiments when the EGR gas is caused to flow through the bypass 15.

(2) Each of the foregoing embodiments has been explained about the case, by way of example, where the inlet port 13 a of the tank 13 opposes only the bypass 15 and the open lower end 13 f of the lower outlet port 13 c of the tank 13 is coincident with the open lower end 15 c of the bypass 15 in the vertical direction. However, the position of the open lower end 13 f of the lower outlet port 13 c of the tank 13 may be different from the position of the open lower end 15 c of the bypass tank 15 in the vertical direction.

(3) FIG. 4 shows a part of the EGR module 7 in another embodiment. FIG. 4 corresponds to the portion near the tank 13 in FIG. 2. In FIG. 4, like reference numerals are used to identify like constituent members as in FIG. 2.

Each of the foregoing embodiments has been explained, by way of example, in the case where the position of the inlet port 13 a of the tank 13 is moved towards the bypass 15 in the EGR module 7 shown in FIG. 6 and the position of the inlet port 13 a of the tank 13 is arranged at the position opposing only the bypass 15.

In contrast, it is possible to employ the construction of the EGR module 7 in which the inlet port 13 a of the tank 13 opposes both the EGR gas cooler 14 and bypass 15 and the position of the inlet port 13 a of the tank 13 is more deviated towards the bypass 15 than the EGR gas cooler 14.

In this case, of the opening area of the inlet port 13 a of the tank 13, the area of the portion 13 h opposing the bypass 15 is greater than the area of the portion 13 i opposing the EGR gas cooler 14. Here, the term “portion opposing the bypass 15” in the opening area of the inlet port 13 a, represents the portion with which a projection image overlaps when the inside of the bypass 15 is projected on the inlet port 13 a in the longitudinal direction of the bypass 15.

Consequently, with this construction of the EGR module 7, it becomes more difficult for the EGR gas flowing from the inlet port 13 a of the tank 13 to impinge against the inlet side core plate 34 of the EGR gas cooler 14 but it becomes easier for it to flow into the bypass 15 than in the EGR module 7 of the prior art shown in FIG. 6 when the EGR gas is caused to flow through the bypass 15. In other words, in comparison with the EGR module 7 of the prior art shown in FIG. 6, the amount of the EGR gas flowing from the inlet port 13 a of the tank 13 and impinging against the inlet side core plate 34 of the EGR gas cooler 14 can be reduced, so that the heat loss of the EGR gas can be reduced, too.

It can be said from the first and second embodiments as well as this embodiment that the inlet port 13 a of the tank 13 may well be arranged at the position at which at least the area 13 h of the portion of the opening area of the inlet port 13 a of the tank 13 opposing the bypass 15 is greater than the area 13 i opposing the EGR gas cooler 14 in order to reduce the heat loss of the EGR gas in comparison with the EGR module 7 of the prior art shown in FIG. 6.

Incidentally, “the position at which at least the area of the portion of the opening area of the inlet port 13 a of the tank 13 opposing the bypass 15 is greater than the area opposing the EGR gas cooler 14” includes the position that does not oppose the EGR gas cooler 1 but opposes only the bypass 15.

It can be said that the area of the portion of the opening area of the inlet port 13 a of the tank 13 opposing the EGR gas cooler 14 in the first and second embodiments is zero and, quite naturally, the area of the portion opposing the bypass 15 is greater than the area opposing the EGR gas cooler 14.

(4) In each of the embodiments described above, the explanation has been given for an example where the inlet port 13 a of the tank 13 is moved closer to the bypass 15 than the position of the inlet port 13 a of the tank 13 shown in FIG. 6.

In contrast, it is possible to decrease the diameter of the casing 21 and to increase the diameter of the bypass 15 while the inlet hole 13 a is kept arranged near the center of the tank 13 in the vertical direction in the EGR module 7 shown in FIG. 6.

It becomes possible in this way to make the area 13 h of the opening area of the inlet hole 13 a of the tank 13 opposing the bypass 15 greater than the area 13 i opposing the EGR gas cooler 14.

(5) Each of the foregoing embodiments has been explained for an example where the downstream portions of the EGR gas cooler 14 and the bypass 15 are connected to the valve housing 17 through the connection joining portion 16 but they may be directly connected to the valve housing 17 without passing through the connection joining portion 16.

In this case, the casing 21 of the EGR gas cooler 14 and the bypass 15 can be integrally brazed or welded to the valve housing 17.

(6) Each of the foregoing embodiments has been explained in the example where the EGR gas cooler 14 is arranged on the upstream side and the bypass 15 on the downstream side, in the vertical direction, but the positional relationship between the EGR gas cooler 14 and the bypass 15 may be changed.

For example, it is possible to arrange the EGR gas cooler 14 on the lower side and the bypass 15 on the upper side, in the vertical direction, though this construction is not shown in the drawing. The EGR gas cooler 14 and the bypass 15 may be juxtaposed in the horizontal direction.

In these cases, the open end of the inlet port 13 a of the tank 13 on the side of the EGR gas cooler 14 and the open end of the bypass 15 on the side of the EGR gas cooler 14 correspond to the open upper end 13 e of the inlet port 13 a of the tank 13 and the open upper end 15 b of the bypass 15, respectively.

(7) Each of the foregoing embodiments has been explained about the example where the exhaust gas flow rate ratio regulating valve 18 and the exhaust gas recirculation rate controlling valve 19 are integrally fitted to the valve housing 17 and the exhaust gas recirculation rate controlling valve 19 is provided to the EGR module 7. However, the exhaust gas recirculation rate controlling valve 19 may be separated from the EGR module 7.

(8) Each of the foregoing embodiments has been explained in the example where the structure having the double poppet valve 53 is employed as the exhaust gas flow rate ratio regulating valve 18 but this structure is not particularly restrictive and other structures may also be used. For example, it is possible to use a so-called “butterfly” structure.

(9) The shape of the tank 13 explained in each of the foregoing embodiments can be changed to other shapes. For example, the shape of the tank 13 may be changed to the shape such that an elbow-shaped pipe can be connected to the inlet port 13 a of the tank 13 shown in FIG. 2, though the construction is not shown in the drawing. In this case, the inlet port of the tank described in the Scope of Claim for Patent means the port 13 a at which the EGR gas starts flowing into the tank 13 in the same way as the inlet port 13 a of the tank 13 shown in FIG. 2 but not the inlet of the elbow-shaped pipe.

(10) FIG. 5 shows a partial sectional view of the EGR module 7 in the second example of another embodiment. Incidentally, like reference numerals are used in FIG. 5 to identify like constituent members as in FIG. 2.

As for the construction of the connection joining portion 16, each of the foregoing embodiments has been explained about the example where the side wall portion 38 on the side of the EGR gas cooler 14, the side wall portion 39 on the side of the bypass 15 and the thickness of the connection portion 40 are decreased and the thickness of the flange portion 37 is greater than the thickness of the connection portion 40, etc. Incidentally, the term “thickness” hereby used means the thickness in the direction vertical to the flowing direction of the EGR gas flowing inside the bypass 15, that is, the thickness in the vertical direction in the drawing.

In contrast, the thickness of the flange portion 37 can be set to be substantially equal to the side wall portion 38 on the side of the EGR gas cooler 14, the side wall portion 39 on the side of the bypass 15 and the connection portion 40 as shown in FIG. 5. Incidentally, the thickness of each of the flange portion 37, the side wall portion 38 on the side of the gas cooler 14, the side wall portion 39 on the side of the bypass 15 and the connection portion 40 is equal to the thickness of the bypass 15 in FIG. 5.

When the thickness of each of the flange portion 37, the side wall portion 38 on the side of the gas cooler 14, the side wall portion 39 on the side of the bypass 15 and the connection portion 40 is reduced in this way, the passage sectional area when the heat moves from the bypass 15 to the outlet side core plate 35 of the EGR gas cooler 14 through the connection joining portion 16 can be reduced. Consequently, heat radiation of the exhaust gas after passing through the bypass 15 can be suppressed.

While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention. 

1. A heat exchange apparatus for an exhaust gas including: a tank which has an inlet port through which an exhaust gas generated by combustion passes and into which said exhaust gas flows from said inlet port; a heat exchanger for an exhaust gas connected to said tank on the downstream side of the flow of said exhaust gas inside said tank, for executing heat exchange between said exhaust gas flowing from inside said tank and a cooling fluid; a bypass connected to said tank on the downstream side of the flow of said exhaust gas inside said tank, for said exhaust gas inside said tank bypass said exhaust gas heat exchanger; and an exhaust gas flow rate ratio regulating valve arranged on the downstream side of the flow of said exhaust gas of said exhaust gas heat exchanger and said bypass, for regulating a ratio of the flow rate of said exhaust gas flowing inside said exhaust gas heat exchanger and the flow rate of said exhaust gas flowing inside said bypass; wherein said inlet port is arranged at a position of said tank at which at least an area of a portion of said inlet port opposing said bypass is greater than an area of a portion of said inlet port opposing said exhaust gas heat exchanger.
 2. A heat exchange apparatus for an exhaust gas according to claim 1, wherein said inlet port is formed in said tank at a position opposing only said bypass of said exhaust gas heat exchanger and said bypass.
 3. A heat exchange apparatus for an exhaust gas according to claim 2, wherein said inlet port is formed in said tank at a position at which an open end of said inlet port positioned on the side of said exhaust gas heat exchanger and an open end of said bypass positioned on the side of aid exhaust gas heat exchanger oppose each other.
 4. A heat exchange apparatus for an exhaust gas according to claim 1, wherein said tank includes a first outlet port to which said heat exchanger is connected, for guiding said exhaust gas inside said tank to said exhaust gas heat exchanger, and a second outlet port to which said bypass is connected, for guiding said exhaust gas inside said tank into said bypass. 